1. Field of the Invention
The present invention relates in general to base transceiver stations of digital mobile telecommunication systems, and more particularly to a base transceiver station of a digital mobile telecommunication system which is separated into a remote site base transceiver station (referred to hereinafter as a remote site BTS) including a radio frequency unit (referred to hereinafter as RFU) and a hub site base transceiver station (referred to hereinafter as a hub site BTS) including components other than the RFU and wherein a base transceiver station interconnection network is used to control the remote site BTS, so that the entire base transceiver station can be installed under the optimum conditions to maximize the quality of speech.
2. Description of the Prior Art
In a digital mobile telecommunication system such as a personal communication system (PCS) or digital cellular system (DCS), generally, a base transceiver station functions to transmit and receive data and voice over a radio channel, control a terminal (e.g., a PCS or DCS terminal), monitor the quality of speech of the terminal and interconnect the terminal and a base station controller (referred to hereinafter as BSC). Namely, the base transceiver station is located between a mobile station and a BSC to interface between wired and wireless channels and perform main functions associated with a radio link. For example, the main functions associated with the radio link may be a function of allocating and managing forward link power to code division multiplex access (CDMA) frequency, channel and frame option resources, a function of processing an outgoing call signal, incoming call signal, soft handoff call signal and hard handoff call signal and a function of receiving and managing global positioning system (GPS) timing information and providing system timing information to the mobile station and base transceiver station.
The base transceiver station is further adapted to perform a function of transmitting and receiving radio signals over a pilot channel, synchronization channel, access channel, paging channel and traffic channel, a function of routing traffic and control information to the BSC and error detection/statistical information collection/report functions.
With reference to FIG. 1, there is shown in block form the construction of a conventional base transceiver station of a digital mobile telecommunication system, which is denoted by the reference numeral 20. As shown in this drawing, the base transceiver station 20 comprises a base transceiver station control processor (referred to hereinafter as BCP) 21 for managing and controlling the entire operation of the base transceiver station 20, a base transceiver station interconnection network (referred to hereinafter as BIN) 22 for performing a packet router function between the base transceiver station 20 and a BSC 10 through an E1 line or T1 line and interfacing high-level data link control (HDLC) packet data between processors in the base transceiver station 20, a time and frequency unit (referred to hereinafter as TFU) 23 for generating a reference frequency and timing synchronization signal to synchronize the processors in the base transceiver station 20 and perform timing synchronization with an adjacent base transceiver station, a digital unit (referred to hereinafter as DU) 24 for modulating and demodulating data and voice signals being transmitted and received over a CDMA channel, and an RFU 25 for converting an ultrahigh frequency (UHF) signal from a mobile station into an intermediate frequency (IF) signal, transferring the converted IF signal to the DU 24, converting an IF signal from the DU 24 into a UHF signal, amplifying the converted UHF signal to a predetermined level and radiating the amplified UHF signal over the air.
A description will hereinafter be given of detailed functions of the above-mentioned components of the conventional base transceiver station 20 of the digital mobile telecommunication system.
The BIN 22 provides an interface with the BSC 10 and an internal communication line to the base transceiver station 20 on the basis of the packet routing function.
The BCP 21 controls and diagnoses the entire operation of the base transceiver station 20 and performs an appropriate operation based on the diagnosed result. Further, the BCP 21 acts to download software associated with initialization of the base transceiver station 20.
The DU 24 acts to process voice and data signals being transmitted and received to/from each terminal. To this end, the DU 24 consists of first and second DUs 24a and 24b as shown in FIG. 1. That is, the DU 24 is adapted to process all signals associated with CDMA.
The RFU 25 includes first and second RFUs 25a and 25b for converting modulated data and voice signals from the first and second DUs 24a and 24b into RF signals, transmitting the converted RF signals to a terminal, demodulating modulated data and voice signals from the terminal, converting the demodulated signals into digital signals and transferring the converted digital signals to the first and second DUs 24a and 24b, respectively. The TFU 23 functions to receive information relating to a reference time necessary to the base transceiver station 20 from a GPS and supply the received information to the base transceiver station 20. As a result, all units in the base transceiver station 20 are synchronized with a GPS time and thus have the same timing.
For the purpose of implementing communication from the BCP 21 to RFU 25 in the base transceiver station 20 of the digital mobile telecommunication system, inter-processor communication of the respective constituting elements must be enabled. For the inter-processor communication, a unique address must be assigned to every constituting element board. Now, a description will be given of a system for assigning addresses respectively to the processors in the base transceiver station 20 and an inter-processor communication system implemented in the base transceiver station 20.
FIG. 2 is a view illustrating a 4-byte address system for inter-processor communication in the conventional base transceiver station 20 of FIG. 1 and FIG. 3 is a block diagram showing a control communication system of the conventional base transceiver station 20 of FIG. 1.
Noticeably, an HDLC packet is used for inter-processor communication in the digital mobile telecommunication system. The HDLC packet is composed of a header and data, which header contains a source address and a destination address. Each constituting element in the base transceiver station 20 of FIG. 1 compares the destination address contained in the HDLC packet header with its unique address and receives the HDLC packet data only when the two addresses are the same. In this manner, the inter-processor communication is made in the base transceiver station 20. Here, the unique addresses of the respective constituting elements shown in FIG. 1 are based on the 4-byte address system as shown in FIG. 2. A hardware address is composed of high-order three bytes of the 4-byte address system shown in FIG. 2 and a software address is composed of a low-order one byte, or fourth byte, of the 4-byte address system.
The hardware address (high-order three bytes) signifies an address that can be set using jumpers on backboards of the respective constituting elements in FIG. 1, and the software address signifies an address that can be assigned according to a program. The hardware address is provided with a BSC identifier (ID), BTS ID, details ID, GCIN ID, test ID and trunk ID. The BSC ID is composed of high-order four bits of the first byte, the BTS ID is composed of the remaining four bits of the first byte and high-order 2 bits of the second byte (six bits in total) and the details ID is composed of the remaining six bits of the second byte. The GCIN ID is composed of high-order three bits of the third byte, the test ID is composed of the fourth bit of the third byte and the trunk ID is composed of the remaining low-order four bits of the third byte.
On the basis of the above address system, the base transceiver station 20 of the digital mobile telecommunication system is provided with an upper block having the above one hardware address and a lower block having only the above software address. The upper block checks a software address in an HDLC packet and distributes HDLC packet data to the lower block in accordance with the checked result. In other words, the DU 24 as an upper block checks a software address in an HDLC packet from the BIN and distributes HDLC packet data to the RFU 25 as a lower block in accordance with the checked result. Namely, if a communication line is connected from the BCP 21 to the DU 24, then the upper block, or DU 24, checks a software address in an HDLC packet inputted via the BIN 22 and distributes HDLC packet data to the lower block, or RFU 25, in accordance with the checked result. As a result, a hardware address is not necessarily required because only the software address of the 4-byte address system shown in FIG. 2 is assigned to the RFU 25 and the DU 24 can receive data. Such a control communication system is shown in FIG. 3. Referring to FIG. 3, the BCP 21, BIN 22, DU 24 and RFU 25 contain processors for controlling the associated units, respectively. That is, the BCP 21 contains a base transceiver station control processor assembly (BCPA) and the BIN 22 contains a high-performance IPC routing node assembly (HRNA). Also, the DU 24 and RFU 25 contain a shelf control and routing card assembly (SRCA) and a transceiver control card assembly (TCCA), respectively.
The TCCA controlling the RFU 25 is connected by wire to the SRCA in the DU 24. If the BCPA in the BCP 21 sends a TCCA control command according to an application program, then the HRNA in the BIN 22 transfers an HDLC packet to the SRCA in the DU 24. Subsequently, the SRCA in the DU 24 checks a software address in the received HDLC packet and compares it with a unique address assigned thereto. In the case where the software address and unique address are the same, the SRCA in the DU 24 transfers HDLC packet data to the TCCA in the RFU 25. Communication from the TCCA to BCPA is advanced in the opposite order to the above flow and a description thereof will thus be omitted.
However, the above-mentioned conventional base transceiver station 20 of the digital mobile telecommunication system is disadvantageous in that all components are installed in one device, resulting in increases in the volume and capacity of the base transceiver station 20.
The increased volume of the base transceiver station 20 makes it hard to choose a place where the base transceiver station is installable and thus install the base transceiver station in a place effecting the optimum propagation.
One conventional approach to solving the above problems is to separate the base transceiver station 20 into a hub site BTS and a remote site BTS including the RFU 25, as shown in FIG. 4. In this approach, because the SRCA in the DU 24 and the TCCA in the RFU 25 are not interconnected by wire, a T1 or E1 line is installed between the TCCA and SRCA and a channel service unit (referred to hereinafter as CSU) or data service unit (referred to hereinafter as DSU) is installed in each end of the E1 or T1 line, thereby performing control communication between the TCCA and SRCA.
The above approach is desirable to readily implement the inter-processor communication by adding the hardware, or CSU/DSU and E1/T1 line, to the existing construction while maintaining the control communication system as shown in FIG. 3 as it is, but disadvantageous in that the above hardware is additionally required with an increase in the capacity of the base transceiver station 20, which leads to an increase in installation cost.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a base transceiver station of a digital mobile telecommunication system which is separated into a remote site BTS including a radio frequency unit and a hub site BTS including components other than the radio frequency unit and wherein the hub site BTS is miniaturized so that the entire base transceiver station can be readily installed under the optimum conditions to maximize the quality of speech.
It is another object of the present invention to provide a base transceiver station of a digital mobile telecommunication system wherein a remote site BTS (including a radio frequency unit) and a hub site BTS (including components other than the radio frequency unit) are interconnected via a T1/E1 line and a base transceiver station interconnection network so that a remote site BTS control system can be modified in a software manner with no addition of separate hardware resources when the entire base transceiver station is increased in capacity.
In accordance with the present invention, the above and other objects can be accomplished by a provision of a base transceiver station of a digital mobile telecommunication system comprising a hub site base transceiver station (hub site BTS) including a base transceiver station control processor, a first time and frequency unit and at least one digital unit and a remote site base transceiver station (remote site BTS), wherein the hub site BTS further includes a first base transceiver station interconnection network for interfacing control data from the control processor to each processor in the base transceiver station; and a first radio interface for transmitting an output signal from the hub site BTS by radio to the remote site BTS; and wherein the remote site BTS includes a second base transceiver station interconnection network for receiving the control data from the first interconnection network and interfacing it to a processor of each constituting element in the remote site BTS; a second radio interface for transmitting an output signal from the remote site BTS by radio to the hub site BTS; a second time and frequency unit for generating a reference frequency and timing synchronization signal to synchronize each processor in the remote site BTS and performing timing synchronization with the hub site BTS; and a plurality of radio frequency units for processing radio frequency signals.